Rosetta - a probe swings by
On 2004-03-04 ESA's Rosetta spacecraft passed the earth at a distance of only 1900km. The close approach made the probe a mag 8-10 object quickly drifting across the sky. Finding the probe was an amateur astronomer's challenge, and the general circumstances of my observing run were quite strange.
I realised that the encounter was up from emails on the morning of March 4. There were finder charts on ESA's website, but only for Leiden (Netherlands) and Frankfurt (Germany), but not for Hamburg. So I made an Ephemeris of the probe using JPL's amazing Ephemeris generator and used the output as a user defined dataset in the star charting program GUIDE 8.0 . This provided me with an excellent finder chart, which I also distributed to several fellow amateurs in northern Germany.
The weather appeared to be non-cooperative. However a check on 20:30 UT revealed that it was clearing up unexpectedly. There was not enough time to get to a darker site, so I had to quickly get started at my city site at Hamburg Altona. This is a very light polluted environment. To make things worse snow was reflecting the city light, and the sky was a bit hazy, so the visual limiting magnitude was 3.5-4.0. I had difficulties to see any stars in Cancer when the probe was crossing this constellation.
My place is in the city center of Hamburg/Germany and
has no free view to the south. Since time was running up I grabbed my Mintron,
fixed a 135mm f/2.5 Pentax lens on it,
put everything on a tripod (no guiding today :-)) and left out. I was lucky not
to run into a police patrol (imagine someone hastyly leaving an appartment
building, having a camcorder and a 12-volt power station in his right hand, a
photo pocket and an SVHS-cable over his shoulder, and a photo tripod with a
camera in the other hand. Also it was extremely cold outside (-5 deg).
After finding a place adequate for viewing I cabled
everything together and powered up the Mintron and the Camcorder. Unfortunately
the sky was extremely bright due to the snow reflecting city lights. I could use
a "sense up" setting of 12 at best (0.24 sek exposure per frame).
Nevertheless a number of stars were visible on the display. I tried 3 times to
get Rosetta into my field of view. With the probe crossing Cancer, I had
difficulties in centering the correct field since no stars were visible to the
naked eye due to light pollution. The first time I lost the race against the
clock (boy is that probe fast!). The second time, at 21:30 when the probe passed
the star 1Cnc (5.9 mag) I was more lucky, I was late but not too late. However I
couldn't see anything moving across the field of the camcorder display. Then I
had to hurry up to center the field of Gamma Gem, which the probe would pass at
21:42. Again nothing conspicious was visible.
Coming home, after 3 cups of hot tea, I started to download the images and stack
them. At first with no success. Next morning I tried to use Fitswork's
comet
guide mode, where the images are centered using a star as a reference, but
displaced from frame to frame to compensate for comets movements. I quickly
estimated the displacement needed in x and y and did the stacking. I first
stacked the Gamma Gem video 30 frames-wise. And BINGO ! the probe was visible on
the stack image, but only faintly. But its movement from stack image to stack
image was consistent, and also perfectly matched the JPL ephemeris track. This
afternoon I tried the procedure with the 1Cnc video.
This one was much easier, since the angular speed of the probe was a bit lower.
Data: 135mm f/2.5, Mintron Camera, stacked with Fitswork, no equatorial
drive whatsoever.